WASHINGTON — Using old mines may be an acceptable way to dispose of the ash from burning coal, but the process needs better monitoring, according to an analysis released Wednesday.

Burning coal produces enough ash to fill one million railroad cars annually in the United States, according to the study by the National Research Council.

Some 38 percent of this ash is used to make cement, wallboard and other products, but the rest is disposed of in landfills and other locations, and increasingly it has been used to refill old mines.

There may be some advantages to this, the report says, such as providing filler for mine reclamation efforts that restore land-use conditions. In addition, the residues may neutralize acid mine drainage, lessening the potential for some contaminants from mines to enter the environment, the report said.

However, the potential for such refilling to expose groundwater to toxic chemicals is not well known, so the council recommended minefills be designed to minimize the movement of water through residues.

It calls for analysis of the residues before they are placed in mines to understand what chemicals they may include, so testing can be conducted for chemicals seeping into the environment.

Currently mines that have been filled are checked by testing the water in wells around the mines. The report urged a more extensive monitoring program, including placing more wells around each refilled mine.

The National Research Council is an arm of the National Academy of Sciences, an independent organization chartered by Congress to advise the government on scientific matters.

Source: Associated Press